Theroux's most recent travelogue is "Deep South: Four Seasons on Back Roads."
MUST-HAVES: I never travel without at least three books, usually novels, not current ones but classics — nearly always paperbacks that I will give away after I've read them. Always a notebook with a good binding. Always two or three pens — specifically Lamy ballpoints. Driving in the deep South for my book, I always had bottles of wine in the back of my car and often food, for those late stops in remote motels where they have microwaves.
COULD USE: Probably a new hat, called the Voyager — made by Lock & Co. Hatters in London. Mine is very battered. You can roll them up and pack them.
TO GIVE: It all depends on the person. For a new friend, perhaps a book of mine related to a distant place, my novel "The Lower River" (set in Africa), or "The Elephanta Suite" (set in India). For an old friend, a classic book, "Madame Bovary." For someone I loved, I would buy a piece of luggage from Glaser Designs in San Francisco.